Voice applications in a telecommunications system including a plurality of conferenced voice channels have several criteria to support while trying to maintain a low Millions of Instructions Per Second (MIPS) footprint and low per-channel end-to-end delay. On the telephony side of the voice application, simultaneous support is needed for narrowband (NB) and wideband (WB) telephony interface devices attached to a modulation bus (e.g., a Pulse Code Modulation (PCM) bus) within a telephony interface (e.g., TDM). On the network side of the voice application, voice channels should transmit and receive voice data encoded and decoded using NB and WB codecs. All channels in the voice application should be able to be conferenced together no matter the operating sampling rates for the telephony side and network side of each voice channel. The operating sampling rate can be either NB or WB.
A voice application's MIPS and per-channel delay performance can be adversely affected by supporting multiple sampling rates at the modulation bus (e.g., TDM) and the network. The addition of the WB sampling rate involves voice channels utilizing upsamplers and downsamplers to convert the samples between the WB rate and the NB rate. The addition of upsamplers and downsamplers to the voice channels has at least two effects. First, the MIPS consumed per channel increases for each upsampler and downsampler used. Second, the end-to-end delay in the voice channel increases with each upsampler and downsampler added within the TX and RX signal processing paths.
An issue that arises when supporting WB and NB simultaneously within the same voice application is the effect upsamplers and downsamplers have on NB channel performance. When dual support of WB and NB channels is added to the voice application the NB channels need upsamplers and downsamplers at all times. The reason for this is, at any time, NB and WB voice channels can be conferenced together. A close operation and then a re-open operation on the NB channel to add upsamplers and downsamplers at the time of the conference is generally not allowed because voice channel statistics and configuration information would be lost.